The proposed program project is based on our central hypothesis that novel signaling pathways are involved in cytoskeletal re-organization upon activation of blood cells. Toward this end we targeted certain relevant genes by homologous recombination: Wiskott-Aldrich syndrome protein (WASP); N-WASP, WASP interactive protein (WIP), Vav 1 and Vav 3, Cdc42 and Rac. We now plan to exploit these "knock-out": to elucidate the pathway(s) from cell surface receptors to cytoskeletal re-organization. The proposal consists of four projects and three cores. Project 1 seeks to understand the overlapping and non-overlapping roles of WASP and N-WASP by identifying their functional domains as well as those of the homologous protein WAVE-2 and to determine the roles of the GTPases, Cdc42 and Rac1, in lymphocyte development and function. Project 2 is devoted to a study of the function of WIP in the control of WASP and N-WASP activation for actin polymerization. Dr. Brugge studies the effect of Vav 1, 2 and 3 on chemotaxis of monocytes and neutrophils. Dr. Rao will study the relationship of calcium flux in lymphocytes to the function of the cytoskeletal pathways in anergy as well as T cell activation. Core A will administer the program.